1. Field of the Invention
The present invention relates generally to a printing method and a printing apparatus. More specifically, the invention relates to a printing method and a printing apparatus for performing printing by ejecting a printing ink and a treatment liquid enhancing printing ability, through a printing head and depositing them on a printing medium.
2. Description of the Related Art
Conventionally, this kind of ink-jet printing method has been utilized in a business machine, such as a printer, a copy machine, a facsimile and so forth, and in an industrial production machine and so forth, in view of low noise, low running cost, easiness in down-sizing of an apparatus, easiness in color printing, and so on.
However, upon printing an image on a printing medium, so-called plain paper by a printing apparatus utilizing the ink-jet printing method, sufficient water resistance cannot be provided for the image and thus the image having high image fastness cannot be obtained. On the other hand, when an image to be printed is a color image, it has been difficult to achieve both of a high density image which does not cause feathering and an image which does not cause bleeding between different colors. Therefore, an image having high image fastness and high image quality cannot be obtained.
As a method for enhancing water resistance of the image, it has been recently practiced to employ an ink containing a coloring agent which is provided with a water-resistance. However, the water-resistance of such ink is still insufficient. Such ink is difficult to solve in a water after drying in principle, plugging of nozzle of the printing head can be caused easily. In order to prevent the apparatus from causing the plugging, a problem to make the construction of the apparatus complicate, can be encountered.
Also, conventionally, there are many publications disclosing technologies for enhancing image fastness of image printed by ejecting a treatment liquid, enhancing printing ability by causing chemical reaction with a printing ink, on the same position as a position where an ink droplet is deposited on the printing medium.
In Japanese Patent Laid-Open Publication No. 58-1288621 (1983), an ink-jet printing method, in which an image position to be printed by an ink is preliminarily identified and the printing ink and a treatment liquid are ejected to the identified position. In the disclosed printing method, printing is performed by ejecting the treatment liquid in advance of ejection of the printing ink, ejecting the treatment liquid overlaying the printing ink which is ejected in advance, or overlaying the printing ink over the treatment liquid ejected in advance and then overlaying the treatment liquid over the ejected printing ink.
In Japanese Patent Laid-Open Publication No. 8-07223 (1996), there has been proposed a method employing means for controlling ejecting the treatment liquid or not. In this method, whether the treatment liquid is to be ejected or not is arbitrarily selected by user, or depending upon a kind of the printing medium.
In Japanese Patent Laid-Open Publication No. 7-195823 (1994), there has been disclosed a method for smoothing the surface of the printing medium by ejecting a colorless treatment liquid in chemical reaction of two or three components on the surface of the printing medium. In this method, remaining amount of the colorless treatment liquid becomes small, printing is performed by scanning of a plurality of times as in the prior art.
However, these publications do not disclose a printing method, which can avoid pollution of an ink ejecting portion and improve reliability of the ink-jet printing apparatus.
On the other hand, in the ink-jet printing system, the following particular problems are encountered.
Namely, since printing is performed by ejecting ink droplets to the printing medium, such as a paper, OHP film and the like, fine ink droplets (mist), generated upon ejection of ink droplets, other than ink droplets depositing on the printing medium and ink droplets (rebounded ink droplets) once hit on the printing medium and then rebounded therefrom, and so on, may deposit on an ink ejection surface of the printing head. A large amount of ink droplets concentrically deposited around the ejection opening, or foreign matter, such as paper dust or the like, is deposited on the deposited ink droplets to interfere ejection from the ink ejecting portion to cause problems, such as deflecting of ink ejection direction from a desired direction (deflection of the ink droplets), causing failure of ejection of the ink droplets (ejection failure) or so on.
FIGS. 1A and 1B are explanatory illustrations showing a process of causing pollution of the surface of the ink ejecting portion by the rebounded ink droplet and the ink mist.
FIG. 1A is an explanatory illustration showing a manner of rebounding of the ink.
An ink ejection head 1 mounted on a carriage has an ink ejecting portion 2 for ejecting an A liquid La and an ink ejecting portion 3 for ejecting a B liquid Lb.
At first, according to movement of the carriage, the A liquid La is deposited on the printing paper 6 as a printing medium. Then, the A liquid La is sequentially spread over a wide area on the printing paper 6. Subsequently, the B liquid Lb is ejected at a certain relative speed in relation to the A liquid La spread over the printing paper 6. As a result, rebounded droplets D.sub.1 of the A liquid La and rebounded droplets D.sub.2 of the B liquid Lb are generated, and these rebounded droplets deposit on the ejection surface of the ink ejecting portions 2 and 3.
FIG. 1B is an explanatory illustration showing a manner of deposition of mist on the ejection surface.
A droplet of the A liquid ejected from the ink ejecting portion 2 is separated into main ink droplet Da and fine ink droplets (mist) M.sub.1. While the main ink droplet Da flies straightly to reach the printing medium 6, the mist M.sub.1 is spread around the flying main ink droplet due to air flow caused by movement of the carriage. The spread mist M.sub.1 of the A liquid is deposited even on the surface of the ejection opening of the ink ejecting portion 3 of the B liquid.
As means for cleaning and removing deposition on the ejection surface, a structure for wiping the ejection opening utilizing a blade formed of an elastic material, such as rubber and the like, is typically employed.
However, when the treatment liquid which causes a chemical reaction with the ink on the printing medium to solidify the ink and make it insoluble, is employed for enhancement of printing ability, the chemical reaction can be caused between the ink and the treatment liquid to set on the ejection surface. Setting can be caused by deposition of the mist or rebounded droplets of the treatment liquid in the vicinity of the ejection opening for the image printing ink and by deposition of the mist and rebounding droplets of the ink in the vicinity of the ejection opening of the treatment liquid. A product generated by chemical reaction of the ink and the treatment liquid has quite high viscosity, it is difficult to remove the product by the normal wiping means. If the deposited liquid droplets cannot be removed, deflection of the droplets and ejection failure are possibly caused. In more worse case to cause greater amount of setting on the head, the head becomes entirely impossible to use.
Pollution of the ejection surface by the rebounded droplets may be avoided by provided greater distance between the surface of the printing paper and the ejection surface (hereinafter referred to as "surface distance"). However, if the surface distance becomes greater, a flying distance and flying period of the liquid droplets are inherently increased to cause degradation of precision of droplets hitting position on the surface of the printing paper and thus to cause degradation of the printed image.
The present invention has been worked out in view of the drawbacks in the prior art as set forth above. Therefore, it is an object of the present invention to provide a printing method and a printing apparatus, which can avoid pollution of an ink ejecting portion and a treatment liquid ejecting portion by mist and/or rebounded droplets of an ink or a treatment liquid by reducing ejection amount of the treatment liquid in a smaller-path printing mode in which printing performance and ejection reliability of the printing head are improved.